Chromium base refractory compositions



2,872,725 Patented Feb. 10, 1959 CHROMIUM BASE nnsnaeronz COMPOSITIONS Edward W. Goliber, Oakiand, Mich, assignor to General Electric Company, a corporation of New York No Drawing. Application May 27, 1954 Serial No. 432,933

6 Claims. (Ci. 29-1825) This invention relates to chromium base refractory compositions consisting essentially of a titanium oxide and chromium, which compositions exhibit properties at normal temperatures, i. e. room temperature, superior to those properties exhibited by sintered commercial grades of chromium.

In view of present industrial needs there is a growing demand for materials having strength, resistance to oxidation at high temperatures, and general chemical inertness. Such materials are required, for example, in the construction of modern aircraft engines, critical furnace parts and critical parts of chemical processing equipment.

It is known that chromium has good strength and resistance to oxidation at elevated temperatures. However, it is exceedingly ditlicult to impart satisfactory room temperature properties to chromium. This is particularly true even when considerable care is exercised in obtaining high purity. Sintered chromium bodies made from commercially available chromium powder containv ing impurities such as oxygen, iron and carbon are likewise weak and brittle.

The present invention is based on the discovery that the room temperature strength of sintered chromium bodies made from commercially available chromium containing the aforementioned impurities may be improved substantially and excellent high temperature properties obtained by the addition of titanium oxides.

Chromium suitable in compositions of the present invention may be commercially available chromium powder containing minor amounts of impurities such as iron, carbon and oxygen.

The titanium of the present compositions may be added to the chromium either in the form .of titanium dioxide or as a lower oxide or suboxide of titanium. Titanium suboxide as hereinafter used refers to oxides of titanium containing less oxygen than is present in the normal titanium dioxide.

When a titanium suboxide is employed in preparing the present compositions, it may be prepared by reacting intimate mixtures of titanium and titanium dioxide in a manner hereinafter described.

Compositions of the invention may be prepared by ball milling pulverulent chromium and titanium oxides, pressing the milled powder into desired shape and sintering in a hydrogen atmosphere under controlled conditions. The milling period employed is dependent in part upon the mill load and upon the initial particle size of the powder.

In compositions of the present invention, the amount of the titanium oxide and of chromium employed may be varied within certain limits. For example, on a weight percent basis, from about 7 to about 40% of an oxide of titanium may be added initially. Chromium powder containing initially about 91% chromium, the balance oxygen and impurities, may be initially added in amounts corresponding to from about 60 to about 93%, by weight of the composition. Oxides of titanium varying initially 2 in titanium content from about to about 85%, by weight, impart the desired properties to the sintered products.

The sintered products of this inventiomcontain more oxygen than is introduced with the oxide of titanium because of the oxygen contained in the finely milled chromium powder which may be as high as 7 weight percent. Because of the oxygen contained in the chromium powder, the sintered products actually may contain'from about 55% to about 85%, by weight, chromium. Taking into account the oxygen contained in the chromium andthe variation in the oxygen content of the oxide of titanium which may be employed, it is seen that the actual titanium content in a sintered product of the invention may vary within certain limits for a given chromium content. For example, in a sintered composition containing 55% chrominum, the titanium may vary from about 24 toabout 33%. Likewise, in a sintered product containing 85% chromium, the titanium may vary from about 4.2% to about 6%, by weight. In compositions containing between 55 to 85% chromium, the titanium content may be varied from about 4.2 to about 33%, by weight, in a comparable manner as is further illustrated in Table I.

TABLE I Percent 55 72 78 24-33 18-24 13-18 9-12 5 4. 2-6. 0 Re- Re- Re- Re- Remetnmaln-'. mairimatnmitlnder der der der det" It is also to be understood that minor amounts of impurities may be introduced in the starting materials and during processing. Iron, in particular, may be present in amount up to about 1%.

Within the above specified chromium limits, are products having maximum room temperature strength. Lower room temperature strength results when either higher or lower chromium contents are employed. Although titanium may be incorporated within the limits specified, the preferred titanium content likewise is nearer the higher limit for a given chromium content. For example, as shown in Table I, a preferred titanium content for a composition containing 72% chromium is about 17% titanium. I

In order that those skilled in the art may more fully understand how the present invention may be carried into.

etiect, the following examples are given by way of illustration and not by way of limitation. All parts and percentages are by weight.

Example 1 A titanium oxide containing approximately 80% titanium was prepared by intimately mixing parts of titanium metal powderand 56 parts of titanium dioxide. Because the initial titanium powder was somewhat oxidized and because some oxidation of the mixed powders results during processing, a lesser amount of oxygen was added in the form of titanium dioxide than ordinarily would correspond to the final oxygen content desired. The resulting mixture was pressed into briquettes which were reacted at 1400' C. in a hydrogen atmosphere and finally crushed and milled to a fine powder.

A quantity of commercially available carbon reduced chromium powder, minus 270 mesh, was milled with acetone for 72 hours, dried and analyzed. An analysis of the milled powder was as follows:

Chromium 90.9%.

Iron 1.5%.

Carbon Less than 1%.

Oxygen About 7% (byditfereuce).

16.8 parts of the titanium oxide prepared above and 63.2 parts of the above milled chromium were intimately mixed by milling with acetone for 72 hours. The" resulting powder was cold pressed at 20,000 p. s. i. and thereafter sintered in a hydrogen atmosphere at about 1475' C. for a period of approximately 30 minutes. The composition of the sintered product is given below:

Titanium 16.7%.

Chromium 72%.

Iron 1.5%. W Carbon About .5%. Oxygen About 9.3% (by ditference).

The product of Example 1 had a transverse rupture strength of 115,000 to 120,000 p. s. i. at room temperature. Good high temperature strength was indicated by the following test based on stress to rupture in cross bending. A bar approximately 1%" x A" x A" was placed on two cylindrical supports 1%" apart. The entire assembly was heated in an air atmosphere to 820 C. and a constant load was applied to thecenter of the bar until it broke. The material so tested had 100 hour strength of 52,000 p. s. i. at 820 C.

Good resistance to oxidation at high temperatures was indicated by the formation of only a very thin oxide film on the surface of the bar after prolonged exposure in an air atmosphere at 8201C.

Example 2 In a manner similar to that of Example 1, a composition was prepared having a higher chromium content as indicated by the following composition:

Titanium 7%.

Chromium 84%.

Iron About 1.5%.

Carbon About .5%.

Oxygen Approximately 7.0% (by diflference).

A sample bar had a transverse rupture strength of 90,000 p. s. i. at room temperature and a 100 hour strength of 58,000 p. s. i. at 820 C. when tested in the manner of Example 1. Improved ductility for this higher chromium content composition was indicated by an approximately 13 degree bend in the bar at 820 C. before C. to about 1550 C. Additionally, inert atmospheres other than hydrogen may be employed. Generally, the usual techniques employed in powder metallurgy for molding or processing of powders are applicable in producing the present compositions.

The novel compositions of the present invention have a wide. range of utility. For example, they may be employed in aircraft engines, in critical furnace parts, in

5. critical parts of chemical processing equipment, etc. Generally, they are useful .wherever strength, resistance to oxidation at high temperature, and general chemical inertness are required.

Sintered refractory compositions consisting essentially of from about 15 to about percent, by weight of the composition of chromium, the remainder being titanium and oxygen in a Ti/O atomic ratio of from about 0.68 to about 1.35, which compositions have high strength and hardness, are the subject matter of and are claimed in my copending application, Serial No. 432,934 filed concurrently herewith, and assigned to the assignee of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A sintered composition having high strength and resistance to oxidation, consisting essentially of chromium and an oxide of titanium, from about to about 85%, by weight of the composition, being chromium,

from about 4.2. to about 33%, by weight of the composition, being titanium, and the balance oxygen.

2. A sintered composition having high strength and resistance to oxidation, consisting essentially of 55%, by weight of the composition, of chromium, from about 24 to 33%, by weight of the composition, of titanium, and the balance oxygen, the oxygen being present as an oxide of titanium.

3. A sintered composition having high strength and resistance to oxidation, consisting essentially of by weight of the composition, of chromium, from about 18 to 24%, by weight of the composition, of titanium, and the balance oxygen, the oxygen being present as an oxide of titanium.

4. A sintered composition having high strength and resistance to oxidation, consisting essentially of 72%, by weight of the composition, of chromium, from about 13 to 18%, by weight of the composition, of titanium,

and the balance oxygen, the oxygen being present as an oxide of titanium.

5. A sintered composition having high strength and resistance to oxidation, consisting essentially of 78%, by weight of the composition, of chromium, from about 9 to 12.5%, by weight of the composition, of titanium, and the balance oxygen, the oxygen being present as an oxide of titanium.

6. A sintered composition having high strength and resistance to oxidation, consisting essentially of by weight of the composition, of chromium, from about 4.2 to 6%, by weight of the composition, of titanium, and the balance oxygen, the oxygen being present as an oxide of titanium.

References Cited in the tile of this patent UNITED STATES PATENTS 2,656,596 Conant et al. Oct. 27, 1953 2,698,990 Conant et al. Ian. 11, 1955 2,783,530 Conant Mar. 5, 1957 FOREIGN PATENTS 645,681 Great Britain Nov. 8, 1950 676,441 Great Britain July 30, 1952 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,872,725 February 10, 1959 Edward w Goliber It is hereby certified that error appears in the printed specifi ication of the above numbered patent requiring correction and that the said Letters .Patent should read as corrected below.

Column 4, lines 26, 32, 38, 44, and 50, for "oxygen", second occurrence in each instance, read titanium Signed and sealed this 29131 day of September 1959.

(SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Oflicer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 2,872,725 February 10, 1959 E r W o Goliber It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, lines 26 32, 38, 44, and 50, for "oxygen", second occurrence in each instance, read titanium Signed and sealed this 29th day of Septemoer 1959.

(SEAL) Attest:

KARL H0 AXLINE Attesting Ofiicer ROBERT C. WATSON Commissioner of Patents 

1. A SINTERED COMPOSITION HAVING HIGH STRENGTH AND RESISTANCE TO OXIDATION, CONSISTING ESSENTIALLY OF CHROMIUM AND AN OXIDE OF TITANIUM, FROM ABOUT 55 TO ABOUT 85%, BY WEIGHT OF THE COMPOSITION, BEING CHROMIUM, FROM ABOUT 4.2 TO ABOUT 33%, BY WEIGHT OF THE COMPOSITION, BEING TITINIUM, AND THE BALANCE OXYGEN. 